What is the minimum gradient for an omnidirectional departure?

The minimum gradient for an omnidirectional departure is indeed 3.3%. This percentage is derived from the required climb gradients that ensure an aircraft can safely clear obstacles in its flight path during the initial phase of departure, particularly when taking off from an airport. The gradient is calculated based on the relationship between the altitude gained and the horizontal distance traveled.

The 3.3% gradient equates to a climb performance that provides a safe margin above the terrain and any obstacles, especially at lower altitudes. It ensures that pilots maintain best performance during the critical initial climbs that are particularly important given the various flight paths an aircraft might take after takeoff.

It's important to note that the other options propound gradients that are either insufficient or above what is mandated for safe omnidirectional departures. These lesser or greater figures do not accommodate the necessary safety margins dictated by regulations for obstacle clearance during takeoff.